Beginning with the discovery of superconductivity in the yttrium, barium, copper oxide, an enormous number of materials have been tested for superconductivity. Although the yttrium, barium, copper oxide material when it was first prepared became superconducting at elevated temperatures, upon examination of the material it was found that the actual superconducting phase was but a very minor amount of the material prepared in bulk. Apparently, the yttrium, barium, copper oxide system is superconducting because the superconducting phase is distributed throughout the lattice structure of the material and is capable of formulating current paths. This is not the case with the Bi, Sr, Ca, Cu oxide system. In the Bi, Sr, Ca, Cu oxide system, it has been found that the material when formulated is intercalated or interleaved. That is material having very low T.sub.c phase is interleaved with a 110 K T.sub.c phase. Because of the interleaving or intercalated nature of the Bi, Sr, Ca, Cu oxide system, it has been impossible to isolate the superconducting phase and more particularly it has been impossible to isolate the 110 K transition temperature material. Heretofore, the Bi, Sr, Ca, Cu oxide material has only shown zero resistance below 100K, typically at 85K due to the inability to segregate the 110K phase.
Accordingly, it is a principal object of this invention to provide a material which has sufficient phase purity to exhibit zero electrical resistance at 110K.
It is also an object of the invention to provide a method of producing bulk quantities of single phase superconducting material.
Another object of this invention is to provide a superconductor consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca and Cu to exhibit a resistive zero near 110K.
Still another object of the invention is to provide a superconductor consisting of a sufficiently pure phase of the oxides of Bi, Sr, Ca and Cu to exhibit a resistive zero near 110K resulting from the process of forming a mixture of Bi.sub.2 O.sub.3, SrCO.sub.3, CaCO.sub.3 and CuO into a particulate compact wherein the atom ratios are Bi.sub.2, Sr.sub.1.4-2.0, Ca.sub.1.8-2.4, Cu.sub.3, heating the particulate compact rapidly in the presence of oxygen to a first elevated temperature near the melting point of the oxides to form a sintered compact, maintaining said sintered compact at the first elevated temperature for a prolonged period of time, cooling the sintered compact and regrinding same to form a particulate material, heating the reground particulate material in the presence of oxygen to a second elevated temperature near the melting point of the oxide, and maintaining the reground particulate material at the second elevated temperature for a time sufficient to provide a sufficiently pure phase to exhibit a resistive zero near 110K.
A still further object of the invention is to provide a method of making a single phase superconductor, comprising formulating a mixture of oxide particulates, rapidly heating the oxide particulates in the presence of oxygen to a first elevated temperature near the melting point thereof to sinter same, maintaining the sintered particulates at the elevated temperature for a prolonged period of time, regrinding and compacting the sintered particulates and reheating to a second elevated temperature in the presence of oxygen, maintaining the reground and compacted material at the second elevated temperature for a time sufficient to provide a substantially pure single phase having a resistive zero at a predetermined superconducting temperature.
The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.